Process of mounting resistance elements of electric heaters



Patented Oct. 1924.

UNITED STATES JQHANN GYURIS, OF BIJ'DAPEST,

HUNGARY, ASSIGNOR TO HUNGARIAN ELEKTHEB- MAX COMPANY LIMITED,

OF BUDAPEST, HUNGARY.

PROCESS OF MOUNTING RESISTANCE ELEMENTS F ELECTRIC HEATERS.

No- Drawing.

To all whom it may concern:

Be it known that I, J OHANN GYURIs, citizen of the Kingdom of v Hungary, residing at Budapest, Kingdom of Hunary, have invented certain new and useul Improvements in Processes of Mounting Resistance Elements of Electric Heaters, of which the following is a specification. My invention relates to electric heaters, such as are used in connection with certain domestic appliances, for example, flat-irons,

toasters and cookers, heaters or radiators,

etc., and consists in a method of so mounting the resistance elements of such devices that they will be more efficient and durable than heretofore.

For the efliciency and durability of electric heaters, it is of special importance that the heat in passing from the heater to the surface to be heated, encounters the least possible resistance. The conse uence of a high re sistance, for instance of t e interposition of an insulating layer of a considerable thickness, is that the heater has to be heated to 5 a point above the working temperature required and is accordingly exposed to a-great heat which results in the premature burning out of the thin wire resistance elements of the heater. Another advantage of facilitating the passage of heat between the heater and the surface to be heated, consists in the heat bein'g rapidly carried away from the resistance element through which the current is passing, whereby it is less exposed to the danger of burning out.

Bearing in mind the above considerations, it has been repeatedly attempted to replace the generally. used heaters, in which the thin metal wire is wound on solid refractory materials or embedded in such materials, the transmission of heat by which is very bad, by other heaters in which the metal wire is in direct contact with the surface to be heated. It has been for instance attempted to put the metal resistance mixed with glass or enamel material, on the insulator, and in some cases on the surface to be heated itself, and to burn it in. Further, a process has been proposed in which the surface to be heated is spread over with easil melting precious metals in varnish-like so ution, the metal separating from the solution only during the burning. The essential disadvantage of this process is that it can be used only with precious metals,

Application filed April 7, 1921. Serial No. 459,346.

but not with the cheaper ordinary resistance metals such as nickel and nickel alloys, owing to which the process is very expensive. Moreover, the process can be used only when the surface to be heated is made of a non.- conducting material, owing to which however the transmission of heat again becomes incomplete. Finally, between the heat expansion coefiicient of the resistance metal and that of its supporting surface, there are considerable differences which result in the resistance element becomingdetached on being heated. Another method of mounting the resistance element consists in embedding it in a plastic vand subsequently setting material, such'as clay or shellac, etc. ThlS process also fails. to give theresult desired, as the material in which the resistance is embedded, always has a heat-insulating effect and thus interferes with the transmission of'heat. Moreover, in this case also the difference in the heat expansion coefficients becomes noticeable. Attempts to select a material for embedding the resistance, the heat expansion coeificient of which is close to that of the resistance, failed to give ya satisfactory result, as it is difficult to find a material of such composition, and also because even when the heat expansion coefiicient of the material agrees more or less with that of the heating resistance, this agreement never exists simultaneously also in re spect of the metal of the surface to be heated. To this must also be added the difiiculty that the material, more particularly when interchangeable heating insertions are used, never fits the surface to be heated accurately, so that the distance between the points at which heat is generated, and the points where it is transmitted, is never the same throughout, and single points of the heating resistance are overheated and burnt out after a short time. 1

All these disadvantages are eliminated by the present invention, which is based on the discovery that the surface to be heated can be utilized directly as a support'for the heating resistance, and that the differences between the various heat expansion coefiicients are equalized by embedding the heating re-' sistance in a thin yielding layer and securing it to the surface to be heated by means of a film-like layer of adhesive. The dis-' tance between the points where the heat is generated, and those where it is transmitted, is thereby rendered sosmall that the heat passes practically unimpeded from the heating resistance to the. material to be heated, and the apparatus built according to the invention shows a particularly high degree of efficiency and a durability by far exceeding that of known apparatus. Owing to the selection of the yielding, preferably felt-like material for embedding, the material can follow all the movements caused by the heating, both of the heating resistance and of the supporting surface, and the layer of adhesive used for securing the material can be so thin that the effect of the differences in the heat expansion coefficients is imperceptible in it.

Exhaustive experiments and measurements have shown that an insulating layer of adhesive of the thickness of 0.03 to 0.05 mm., together with a layer of an embedding material which is 0.1 to 0.5 mm. thick and also insulating, is suficient for ensuring a complete insulation for instance at 110 volts and at a temperature of. 600 0., whilst hitherto for the same purpose insulating bodies at least 1 to 8 mm. thick had to be used. Owing to the metal wire, constituting the heating resistance element,being heated .only to a few degrees above the desired working temperature, the transmission of heat taking place quite directly, the strain on the metal wire at the same working temperature is considerably less, and its durability exceeds that of the old heaters considerably.

For securing the embedding material, any insulating adhesive that adheres well both to the surface to be heated and to the embedding material, can be used. A very dilute solution of equal parts of water and water glass, containing in suspension finely ground clay, kaolin, asbestos powder, etc., has proved particularly suitable. A filmlike layer of such a glue has the property of adhering fast and of following any expansions and warping of the supporting surface, without becoming detached or cracked.

The expanding, preferably felt-like embedding material must be electrically insulating and fireproof. These conditions are best fulfilled by asbestos paper of a thickness of 0.1 to 0.5 mm. Asbestos paper has further the advantage that it can be made of absolutely uniform thickness, so

that the heating resistance is at every point at the same distance from the surface to be heated. The resistance wire is for instance secured to a layer of asbestos paper by using templates and then covered with a similar second layer of asbestos paper. The two layers of asbestos paper might be stuck together and preferably by means of the above mentioned adhesive consisting of water, water glass and clay, etc. The embedding material is then secured by means of a thin layer of adhesive to the surface to be heated. The securing is preferably effected under pressure and with heating, ow-

ing to which the excess of adhesive is expressed or evaporated. One layer of. the

yielding embedding material might also be I of the two layers of the embedding material is not required, but nevertheless when using asbestos paper, it is advisable to moisten it. The embedding material insulates the coils of the heating resistance from each other and fromthe surface to be heated, and prevents oxidation of the resistance.

Before putting on the adhesive, it is advisable to clean the surface to be heated from any impurities, more particularly from grease, in order to ensure good adhesion.

The construction of the heater according to this invention may be for instance, carried out in the following manner.

The surface to be heated is cleaned and coated with a layer of adhesive, This layer,

while still moist, is covered with a piece of thin (0.1 to 0.5 mm. thick) asbestos paper which is preferably moistened or coated with the adhesive and must cover those places where the metal wire forming the resistance is to be placed. The metal wire put in place is covered with another layer of asbestos paper, and the two layers of asbestos paper are carefully smoothed out in order to remove any air. The ends of the metal wire, which were already provided with thicker contact parts which are good conductors of current, are secured, with the use of thicker asbestos paper and of the same adhesive, to

the surface tobe heated. After the metal wire has been secured, the whole surface to be heated, or the whole apparatus, is sur rounded, before the adhesive and the layers of asbestos papers become dry, from the outside with a thicker (about 5-30 mm. thick) layer of asbestos powder or sand, placed in suitable moulds into a press .under pressure slowly allowed to dry and finally heated to 1501000. After the burning, it is preferable to pass the current through the metal wire for a certain length of time. The layer of asbestos powder or sand assists quick absorption of the moisture, and uniform transmission of the pressure.

When making flat heaters, such as flat irons, level radiator surfaces, cooking range plates,etc., the metal wire to which has been gives the proper shape, may also be secured to asbestos paper, either by sticking, for instance with the above mentioned suspension of clay, etc., in a mixture of water and water glass, or b threading through, or by sewing on with t irea'ds which are destroy-ed during the heating, etc. The metal wire is then covered with a second layer of asbestos paper. The surface to be heated is coated 1n the manner described with a layer of adhesive, whereupon the layers of asbestos are insulated from each other as well as from the surface to be heated. This gives a membrane-like heating body, the thickness of which scarcely exceeds that of the thin (about 0.2 mm. thick) metal wire constituting the heating resistance. The insulating layer of this heater is therefore extraordinarily thin, owing to which the trans mission of heat is almost as perfect as if the heating resistance were secured direct to the surface to be heated, while owing to the good transmission of heat, any overheating and burning out of the heater do not take place even when the heater apparatus into which the heating body is built, is standing for a long time under current. The heating body is perfectly soft, flexible and elastic,

so that it fits completely any bends, uneven portions of the surface to be heated,.which is of paramount importance as regards the transmission of heat. The heating resistance is completely embedded in the insulating material, owing to which the heating resistance is firmly heldin its position by the insulating material itself, and the insulating material encloses the heating resistance in a perfectly air-tight manner, so that no oxidation of the heating resistance can take place. The air-tight arrangement does not in any way affect the flexibility of the heater.

In manufacturing the heater, the proceeding may be such that the metal wire con stituting the heating resistance, is wound on one of the insulating platesin the form of fiat windings, the resistance is then covered with the second insulating plate and the whole pressed together, so as to produce a heater which is very thin and flexible.

The insulating plates may be made of any thin flexible or yielding insulating material. It has been found particularly advantageous however to use asbestos paper in which the windings of the metal wire are embedded during the pressing. Other insulating substances may however also be used, but if complete connection of the insulating plates and the heating resistance cannot be obtained by compression, the heating resistance must be held fast between the insulating plates by a binding means. As already stated, this binding means may be the above mentioned adhesive. The use of such a binding means is moreover advantageous even when the heating resistance is placed between two insulating plates such as asbestos paper, as it improves the strength of the connection and ensures better insulation. When a binding means is used, the heater is dried before or after pressing.

When using suitable insulating materials, the heating resistance may be placed in them durin the manufacture of the insulating materia s.

The winding of the metal wire, the drying and the pressing may be effected in any desired manner. Between the insulating layers may also be placed several heating resistance which may then be connected in series or in parallel. During the winding, care must be taken to leave free the two ends of the metal wire. These two ends of the wire may be if necessary soldered to contact plates, corresponding recesses being formed in the heating apparatus, so that the said heater is at once ready after the contacts are inserted.

The thickness of the heating bodies connected in the above manner to the surface to be heated, is very small (0.4-0.5 mm.) so that the best possible transmission of heat is obtained. The heating bodies are not sensitive to variations of the outside temperature, they are extraordinarily fireproof and retain their insulating capacity without change even at high temperatures.

According to this invention, existing apparatus, for instance ordinary cooking vessels, pots (enamelled or otherwise), gas and coal flat irons, etc., may be adapted in a simple manner for electric heating.

What I claim is:

1. The method of mounting the resistance elements of electric heaters, which consists in embedding the same in a yielding insulating fireproof material, and securing the latter to the surface to be heated by a thin layer of insulating adhesive substance.

2. The method of mounting the resistance elements of electric heaters, which consists in securing them between two layers of asbestos paper by means of an insulating adhesive.

3. The method of mounting the resistance elements of electric heaters, which consists in attaching them, by means of an insulating adhesive substance, to a yielding sheet of insulating material, and securing the latter to the surface "to be heated by means of said adhesive substance.

4:- The method of mounting the resistance element of an electric heater, which consists in securing it on a sheet of asbestos paper by means of an insulating adhesive, and

in securing it to a sheet of flexible insulating fireproof material by means of an adhesive of water, water glass and a refractory powder, and securing said sheet to the surface to be heated by ineans of thesame adhesive substance.

6. The method'of constructing a resistance element, which consists in securing it to asbestos paper by means of an insulating adhesive substance, whereby said element can ture.

JOHANN GYURIS.

vbe applied to any desired surface to be: 

